The present invention relates to indenylidene compounds, and an electrophotographic photoconductor which comprises a photoconductive layer containing at least one of the benzylideneindene compounds.
Examples of photoconductive materials for use in the conventional photoconductors for use in electrophotography are inorganic materials such as selenium, cadmium sulfide and zinc oxide. In an electrophotographic process, a photoconductor is first exposed to corona charges in the dark, so that the surface of the photoconductor is electrically charged uniformly. The thus uniformly charged photoconductor is then exposed to original light images and the portions exposed to the original light images selectively become electroconductive so that electric charges dissipate from the exposed portions of the photoconductor, whereby latent electrostatic images corresponding to the original light images are formed on the surface of the photoconductor. The latent electrostatic images are then developed by the so-called toner which comprises a colorant, such as a dye or a pigment, and a binder agent made of a polymeric material; thus visible developed images can be obtained on the photoconductor.
Fundamental characteristics required of the photoconductor for use in electrophotography are: (1) chargeability to a predetermined potential in the dark; (2) minimum electric charge dissipation in the dark; and (3) quick dissipation of electric charges upon exposure to light.
While the above-mentioned inorganic photoconductive materials have many advantages over other conventional photoconductive materials, they also have several shortcomings.
For example, a selenium photoconductor, which is widely used at present and sufficiently meets the above-mentioned requirements (1) to (3), has the shortcomings that its production conditions are difficult and, accordingly, its production cost is high. Further it is difficult to work it into the form of a belt due to its poor flexibility, and it is so vulnerable to heat and mechanical shock that it must be handled with the utmost care.
Cadmium sulfide photoconductors and zinc oxide photoconductors are prepared by dispersing cadmium sulfide or zinc oxide in a binder resin. Therefore they are so poor in mechanical properties such as surface smoothness, hardness, tensile strength and wear resistance that they are not suitable as photoconductors for use in plain paper copiers in which the photoconductors are used in quick repetition.
Recently, varieties of the organic electrophotographic photoconductor have been proposed to cover the shortcomings of the inorganic photoconductor, and some of them are in fact put to practical use. Representative examples of the organic electrophotographic photoconductor are an electrophotographic photoconductor comprising poly-N-vinylcarbazole and 2,4,7-trinitrofluorene-9-on (U.S. Pat. No. 3,484,237), a photoconductor in which poly-N-vinylcarbazole is sensitized by a pyrylium salt type dyestuff (Japanese Patent Publication No. 48-25658), a photoconductor containing as the main component an organic pigment (Japanese Laid-Open Patent Application 47-37543), and a photoconductor containing as the main component an eutectic crystalline complex made of a dye and a resin (Japanese Laid-Open Patent Application No. 47-10735).
Although the above-mentioned organic electrophotographic photoconductors have many superiorities for practical use compared with other conventional photoconductors, they do still not satisfy all the requirements of the electrophotographic photoconductor.
The previously mentioned electrophotographic photoconductors, which are different in the application and the preparation method thereof, can generally show excellent properties when the superior electroconductive material is used.